The present invention relates to a puncture-sealing pneumatic tire provided with a layer which prevents the leakage of air when foreign substances, such as nails and the like, on the road are penetrate through the tread of the tire during running, and to a method for producing such a tire.
In order to avoid tire puncture deflation there has been proposed a pneumatic tire provided with a puncture-sealing layer formed of a thin viscous rubber layer adhered integrally to the inner peripheral surface of the tire at the backside of the tread portion. This pneumatic tire is generally produced in the following manner. A thin rubber sheet, which is not hardened and elasticized even by heating and which has a width sufficient to cover the tread portion of a tire, is used as a puncture-sealing layer, and is firstly wound up on a cylindrical green tire-former at a position corresponding to a tread portion of the tire, and then other members for constituting the tire are successively superposed thereon to produce the green tire. This method is advantageous in that even when a green tire produced thereby is made hard and elastic by vulcanization, the puncture sealing rubber layer is formed at a given position of the inner peripheral surface of the tire with a certain constant thickness while maintaining its viscosity. Therefore, even when foreign substances penetrate through the tread of the tire during running, the viscous rubber layer surrounds the foreign substances and the air in the tire does not leak. Moreover, even when the foreign substances fall out from the tread due to centrifugal force caused by the rotation of the tire, the viscous rubber flows into the holes left and tightly closes them and as the result the tire remains air-tight. However, in this method, pneumatic tires having a desired high puncture-sealing ability have not yet been obtained.
The reason is as follows. When a viscous rubber layer having the ability to catch and retain nails by adhesion is used, it moves towards and accumulates in the center portion of the tread due to the lowering of its viscosity and centrifugal force, which are caused by heat accumulation in the tire and the temperature rise of the tire during running. As the result, the viscous rubber is localized to lower the desired performance of the tire and cause unbalance in rotation, and the tire cannot be often driven safely. In order to prevent the moving and accumulation of the viscous rubber, a cover layer and a honeycomb-shaped layer for preventing the movement of viscous rubber must be arranged in the puncture-sealing layer. However, the movement of viscous rubber cannot be completely prevented. On the contrary, when a hard viscous rubber layer having poor flowability is used, the adhesion of the rubber layer to foreign substances, is poor.
Further, it is indispensable for the puncture-sealing layer that it maintains a predetermined performance throughout high temperature and low temperature, that the layer is not oxidized and deteriorated by air at high temperature and under high pressure, and that the layer does not deteriorate the other materials constituting the tire.